WIP: GroupchatControl: Add group chat info popover and display JID in banner

This adds a second label to show the group chat's name and the JID.

Additionally, the avatar is sized like in the single chat window.

The subject popover is replaced by a room info popover displaying the following group chat infos:

• Title
• JID
• Description
• Subject
• Access
• Password protection
• Anonymity
• Persistence
• MAM
• Language

This depends on !459 (merged).